Alcoa of Australia Residue Management
 
Residue Reuse
As a leader in sustainability, Alcoa of Australia is committed to ensuring sustainability principles are applied to the management of bauxite residue.  Our efforts in residue reuse research are far ahead of any of our competitors, and we are leading the industry in terms of promoting this as a key sustainability issue for our industry. 

Alcoa in WA refines bauxite into alumina, and the residue remaining after this process takes place is compromised of two primary components of roughly equal quantity – sand and mud.

Through research spanning over 20 years, Alcoa has identified a number of possible sustainable uses for bauxite residue. This work has been carried out by Alcoa’s refining research and development team, the Technology Delivery Group (TDG), which supports the business globally and is based at Kwinana Refinery in Western Australia.  

While 20 years ago our research was driven by a desire to reduce the size of our residue areas - a goal shared by our local communities - the opportunities coming from residue reuse have become much broader with several exciting possibilities. Read more about these possibilities below.

In addition, Alcoa was a foundation member and key industry supporter of the former WA-based Centre for Sustainable Resource Processing (CSRP), which facilitated a great deal of further research into residue reuse. Trials facilitated by the CSRP consistently showed bauxite residue has the potential to become a useful material. 

The potential uses for the sand and mud components of our bauxite residue include:

  • As a soil amendment for broad use acre farming and horticultural uses;   
  • As a sand for use in cement manufacture;   
  • In effluent treatment ponds and septic systems;   
  • For trace metal retention from road runoff, rubbish tips and acid mine drainage;   
  • In ceramic manufacturing;   
  • In plastics manufacturing; and  
  • For use as a road base.
     
The three most promising bauxite residue by-products are: Red Sand™, Red LimeTM and Alkaloam®.

Red Sand™
TDG has developed a carbonation and wash system to process residue sand, producing a by-product now known as Red Sand.  Red Sand is literally crushed rock that is red in colour.  

Testing shows Red Sand can be used as a general fill material, as construction backfill or as a material suitable for road base construction. 

There is evidence to suggest sand supplies, particularly in the South-West of WA, are in decline and Australian construction companies are looking for alternatives. Alcoa’s Red Sand has the potential to fill this need. 

Not only does Red Sand have the potential to be a cost effective alternative to general purpose sand, it has also shown to be a high quality construction sand thanks to its excellent drainage and strength characteristics.

Commercialisation of sand from residue would have a range of potential benefits including:

  • as a viable substitute for increasingly scarce supplies of quarry sand;  
  • reducing the clearing of natural bushland for sand quarries; and  
  • reducing the requirement for residue storage facilities.

The carbonation and wash process used to treat residue sand removes most of the remaining carbonate salts making the end product (Red Sand) environmentally benign.  The classification of the components of Red Sand, by Safe Work Australia (national occupational health and safety authority, responsible for setting national standards and codes in this area), is consistent with the classification for all sand products sold in Australia.

The Perth to Bunbury Highway road network, which opened in 2009, incorporated more than 2500 cubic metres of Alcoa’s Red Sand as part of road base to widen the Greenlands Road access to the new highway near Pinjarra.

The successful future commercialisation of Red Sand will fill a gap in the marketplace and fulfil Alcoa’s strategic goal to reduce the size of our residue areas.
 
Red LimeTM 
Red Lime is a by-product removed during the refining process that is then washed and dried. 

Red Lime has a high acid neutralising value and therefore has applications in pH control in agriculture or industrial systems. Red Lime could be more effective than most available pH control products because of the fine particle size and sodium carbonate that remains with the product. Work is continuing to evaluate the feasibility of producing a Red Limeby-product, with the initial focus on use as an agricultural lime.
 
Alkaloam® 
Alkaloam is the registered trademark of Alcoa produced red mud.  Alkaloam is the fine-grained residue which is carbonated through a reaction with carbon dioxide.  

In 1993, a proposal for the use of Alkaloam in the Peel-Harvey coastal plain catchment for trial projects was submitted to the Environmental Protection Authority, by the then Department of Agriculture, and approved (this followed a Public Environmental Review).  Since then, trials have consistently demonstrated there are real benefits of adding Alkaloam to sandy soils which are common in coastal regions of Western Australia.  Alkaloam has proved successful as a soil amendment for nutrient deficient, acid soils and can increase the productivity of farmland.  When excess nutrients from farmlands reach our waterways, it can cause serious environmental problems - but Alkaloam use on farmlands has shown to reduce the amount of excess nutrients reaching waterways. In addition, Alkaloam prevents phosphorous from being washed from farms into water channels, ultimately helping to prevent algal blooms and fish kills.
 
Alkaloam is alkaline which increases soil pH in the same way as agricultural lime.  While traditional lime can take a number of years to effectively reduce the pH of soil, Alkaloam can achieve this same result almost straight away.  Therefore, Alkaloam allows farmers to gain maximum benefits from the adjustment in soil pH far sooner than waiting for a soil response over one or more rainy seasons.

An assessment of the sustainability attributes of the product were comprehensively evaluated by the Centre for Sustainable Resource Processing (see below).

Alcoa’s Residue Reuse Direction
At present Alcoa of Australia is focused on the commercialisation of Red Sand, as opposed to Alkaloam or Red Lime, because Red Sand is the by-product with the most potential alternatives uses. 

Alcoa is of the view that a broad regulatory framework should be established to guide the assessment of the suitability of these types of materials, and to ensure the scientific rigour to support that assessment. We believe this will help encourage research and the adoption of sustainable minerals processing.

Alkaloam Sustainability Assessment
Alcoa suggested to the CSRP that it conduct a Sustainability Assessment of Alkaloam.  As a strong supporter of sustainable minerals processing, and the re-use of mineral processing by-products, Alcoa considered that a broad Sustainability Assessment would help inform the debate about Alkaloam.

In 2008, following Alcoa’s suggestion, the CSRP commissioned an assessment looking at the use of Alkaloam in the Peel Harvey catchment. 

The final report provides a consolidated review of all the available studies into Alkaloam, and an assessment of the potential benefits and costs of the commercial use of the product. 

The final report stated:

“There is adequate research and evidence to support claims that Alkaloam increases plant growth. The net value from improved agricultural productivity in the Peel Harvey area, with the application of Alkaloam, has been estimated to be worth some $40 million over 25 years.”

“In summary, the literature review shows that there is no evidence to suggest that Alkaloam is unsafe.”

“This assessment indicates the use of Alkaloam as an agricultural soil amendment in the Peel-Harvey catchment will produce a net economic benefit to the community, valued at $70 million over 25 years. It should provide productivity benefits to farmers, provide a cost effective approach to reduce exports of phosphorus from agricultural soils and reduce environmental impacts. Use in the Peel Harvey area only will only provide a minimal reduction in the area required for, and cost of, bauxite residue storage.”

Residue Carbonation – ‘Carbon Capture’ Technology
Alcoa currently has a full scale ‘Carbon Capture’ plant in operation at the Kwinana Refinery in Western Australia. This unique process mixes carbon dioxide (a greenhouse gas) with bauxite residue to reduce the alkalinity of the material, thus reducing residue drying time, and providing a sink for what is usually a waste gas released into the atmosphere.  As well as reducing greenhouse gas emissions, other flow on benefits include:

  • Decreased potential for groundwater impact; 
  • Decrease in the area required to dry mud;  
  • Decreased risk of dust lifting from carbonated residue; and 
  • Creation of more opportunities for residue reuse.

Kwinana’s ‘Carbon Capture’ plant has the capacity to lock up 70,000 tonnes of carbon dioxide each year.
 
Through our membership of the Kwinana Industries Council in WA we continue to contribute to research into how Kwinana industries can achieve ‘waste’ synergies by using each others’ by-products - carbon capture is one of those ways. The plant locks up carbon dioxide from a nearby ammonia plant, demonstrating how industry can form sustainability partnerships to reuse waste products.
 
While we are working towards implementing this technology in all of our refineries, a carbon dioxide source is needed for the process to take place.  At Kwinana the nearby ammonia plant is the carbon dioxide source, however there are no similar sources near our other WA refineries.  Alcoa is working towards being able to use our own carbon dioxide in the carbon capture process and the technology needed to do that is in development.
 
For more information on Carbon Capture click here.


• Media Release May 2010: Alcoa puts by-product to sustainable use
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• November 2009 Alcoa Community Enews: Turning Alcoa sand into a valuable product
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• August 2009 Alcoa Community Enews: R&D the key to our sustainable future
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